The present invention relates to a single reflex camera and more particularly to a drive mechanism of a single reflex camera which enables a photographic object to be viewed in a bright condition immediately before and after exposure.
These drive mechanisms control the operation of a movable reflecting mirror and a diaphragm of an objective lens. In previously known arrangements of such drive mechanisms, the movable reflecting mirror has a normal tendency to be moved to its viewing position, while the diaphragm for the objective lens, which has a normal tendency to be stopped down, is maintained in its open position against its normal tendency. Immediately before an exposure operation, the reflecting mirror is moved from its viewing position to its picture taking position in association with initiation of the releasing operation of a shutter. The diaphragm is then stopped down from its open position to its pre-adjusted diaphragm aperture, after which the shutter is released to commence with exposure. After completion of the exposure operation in association with completion of the travel of a rear curtain, the movable reflecting mirror is returned to its viewing position to again enable viewing of an object in a bright condition. The diaphragm is then returned from its pre-adjusted position to its open position.
The prior art drive mechanism of the type described, however, drives the movable reflecting mirror and a diaphragm only by means of a single drive mechanism. As a result, in the return travel after the exposure operation, when the diaphragm is driven to its open position by the spring member, the returning or restoring force of the spring member is added through the drive mechanism to the force of the movable reflecting mirror returning to its viewing position. For this reason, when the movable reflecting mirror stops in its predetermined viewing position, there is still exerted a large moment inertia on the mirror, which causes difficulties in stopping the mirror in its predetermined position in a stable manner.